【转帖】position tolerance

yang686526

position tolerance
i have given gd & t condition for mount hole location -
1st box having diametric tolerance of 5 mm & three more box with datum a, b & c. (there is no max or min material condition). also, there is a basic dimension from datum a,b,c to hole. the hole dia is 25 mm, making the hole through drilling process to the plastic.
(a)now, i was wondering is it possible of 5 mm diametric position tolerance for 25 mm hole? don't think its too much?
(b)if the hole centre has position tolerance than how does it will maintaion the basic dimension from datum a,b,c?
the tolerance allowed is a function of the interfacing components and the tolerances allowed on them.  there is a formula for determining the tolerance allowances.
what version of the standard was applied to the drawing in discussion?
ringman
if i understand the question, the ans is asme y14.5, drafting standards
if you have a positional tolerance of a diametrical tolerance zone of 5 mm on a drilled hole in rfs, it does seem a bit large but maybe the hole is not important (shouldn't use gd & t then). it all depends upon its function.
basic dimensions are theoretical dimensions with the tolerance given in the feature control frame (box).
by the way, since there is no mmc, then there is no checking fixture. one must confirm the centre lines of the hole probably using a cmm or other measuring methods.
dave d.
if you're not sure how to correctly apply gd&t to this drawing i would leave it off.  i would suggest if you're interested in apply these principles to future designs that you get some formal training otherwise it could be a costly lesson.  there are a lot of resources out on the net for you to learn.
heckler
sr. mechanical engineer
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(in reference to david beckham) "he can't kick with his left foot, he can't tackle, he can't head the ball and he doesn't score many goals. apart from that, he's all right."  -- george best
i agree with heckler. do not apply any gd & t unless you have been fully trained and are confortable with it. there are too many confusing drawings out there that cause grief to manufacturing and quality.
dave d.